Abstract: Theoretical analysis and experimental study of the bending vibration of DFB (Distributed Feedback) fiber laser in the underwater sound field are carried out.The calculating expression of the acoustic pressure sensitivity of the DFB fiber laser hydrophone,whose signal is demodulated by an unbalanced interferometer system,is concluded.And based on the theory of beam,the sensitivity in the frequency range of 50 to 2000 Hz of the DFB fiber laser,both ends of which are fixed,is calculated out by numerical method.And accordingly,the frequency-response curve is figured out.A DFB fiber laser hydrophone is experimentally studied in the frequency range,the experimental data is repeatable and in good agreement with the theoretical results.It is indicated that the DFB fiber laser is ready to be induced with bending vibration by ambient disturbance in underwater sound field,due to its thin and lengthy configuration.And along with that,vibration noise will be led into the signal output of acoustic pressure,and as a result,the acoustic characteristics of the DFB fiber laser will be influenced,and in the design of DFB fiber laser hydrophone unit,the influence should be taken into account.